Apparatus for heating gas streams



y 1945- L. SILVER ET AL 2,375,500

APPARATUS FOR HEATING GAS STREAMS Filed Oct. 2, 1940 Q 2 Sheets-Sheetl y1945- L. SILVER ET AL 2,375,500

7 APPARATUS FOR HEATING GAS STREAMS Filed Oct. 2, 1940 v 2 Sheets-Sheet2 process.

Patented May 8, 1945 2,375,500" APPARATUS ronaimn'rmocss STREAMS LeonardSilver and Michael Maocormac,jLondon,

England, assignorsto The Gas Light and Coke Company, Westminster,

British company,

London-England,- a

Application October 2, 1940, Serial-No. 359,462

In Great Britain October'Q, 1939 a c n; (01. s-+190 This inventionrelates to a method'andapp ratus for heating a stream of combustiblegas. For example it maybe necessary in certain catalytic reactionsinvolving gases to preheat thegas or mixture of gases in order toinitiate 'the catalytic reaction. 01', again, in certain instances, a

reaction between gases may be self-supporting once the gases have beenraised toa certain tem:

' perature, as, for example in'theFi'scher Tropsch For such purposes,the heating of the gases can bediscontinued-after the reactionhas Iprise a nozzle which is directed into the endpof v of air a'ridtoreintroduce the mixture; into; the

supplyconduit, p i

The aforesaid compressed air ejector may coma" mixing passage whichcommunicates with said combustion chamber and the inlet end of whichpassage also communicates with the chamber or conduit. 1 For example,the nozzle may be located in an inlet chamber which communicates withbeen initiated. The invention is'also applicable .to gas purifierswherethe impuregas requires 7 to' be brought to a certain temperature inorder to maintain the activity of the purifying mate'- rial which, forexample, may comprise iron *oxide. In attempting to heata stream of gasby intro ducing a limited supply of air locally into a "gas stream andigniting it, it is found'that there is a tendency for the resultingflame to be unstable and also to form soot which is deposited in theplant or on the catalyst. An object ofthe'present invention istoovercome these disadvantages.

According to this invention a method ofheating a streamof gas consistsin withdrawing irom the maingas stream a quantity of gas which is mixedwithair for combustion, and re-introduc-.

ing the mixture locally into the gas; stream, either directly, or incases where soot'deposition, is likely. to occur through a combustionchambery and in igniting the mixture inv the combustion,,,chamher or gasstream. The amount. of 'gasjin the mixture may range from a'deficiencyto aslight excess of that which would be required for com! pletecombustipn with the.air,. By .these'means it is possible to control theratio of gas andair in the mixture to be burnt and thereby provide astable flame and prevent the formation of soot],

The required quantity of gas maybe withdrawn from the gas'stream by theejector action-Di a the mixing passage and also communicates throughaninlet conduit with said supply conduit. The: inlet chamber may belocated eitherinside or outside said'su'pply conduit.

- In-order'that the ratio of gas and arinthe v f mixture may beaccurately controlled," the aforesaid -inlet conduit may be providedwith a-con-j trol valve; or the passage may be'provided with acalibrated restriction, or the distanc'e'between the injector nozzle andthe throat'may' bevaried;

In an apparatus embodying a combustion: chamber, said chambe'r may bearrangedto ex-.

tend in an axial direction within the .supply conduit and is providedwith an open end 'so" as to,

a direct the burning mixture in the same direction as the flow: of themain gassupply. For example,- the combustion chamber may becylindrical-in shape and arranged co-axially with thesupply conduit; i

In any of the arrangements referred-toxabovethe mixing passage may beventuri in shape.

The outlet end of the'mixing passage maycomprise a nozzle which projectsinto the cylindrical" combustion chamber.

supply of :compressed air which is also utilised for the combustion ofthe withdrawn gas. f i

An apparatus according to this inventionthus comprises meansfor-withdrawing from the main gas'stream a quantity of gas toprovide'therequired amount: of heat for heating the gas stream, means for mixingthe withdrawn gas with air for its combustion and means forreintroducing the mixture locallyinto thegas' stream either directly orthrough a combustion chamber and means for igniting the mixture, iindicated above, a compressed'air ejector may be, arranged to effect thewithdrawal of the 'gasiromvthe gas-stream, to-mix it with the requiredamount In'such an arrangement, the gasmixture either burns at thenozzleor at some intermediate" point between .it and the open end of thecombustion chamber, a 1? In a simple form of apparatus according to thisinvention, the combustion chamber may. be. lo-

cated within the supply conduit and thewalls thereof maybe providedwitha number of ports and the aforesaid air ejector nozzle may ice-arrangedto "project into the combustion chamber in the neighbourhood of saidports. Thus, a proportion of the gas stream. is' drawn through the portsinto the combustion chamber by the ejector actionofsaidnozzle.

i The aforesaid combustion chamber and/or the v mixing passageassociated with it may be-so shaped'thatthe velocity of thegas-air'mixture,

afterleaving'the nozzle, decreases until it isapproximately equal totherate of propagation of a flame in themixture. 1

In any 'ofthe arrangements referred to' above, a-flametrap sucha's ametal spiral, a wire'gauze,

a porous refractory partition, a perforated plate, or a, grid may bedisposed either at the inlet end of the combustion chamber or within theI combustion chamber.

' The air pressure requires to'be greater than that of the gas supply.The amount of gas in the mixture may be slightly in excessof that-whichwould be required for complete combustion with I the air supply, but notsufficient to cause $0013..

The ignition of the mixture may be eifected either directly or via apilotjet by means of. a i

wire formed from a'platinum or nickel-chromium all'oyjwhich iselectrically heated and-whichis disposed near the outlet end of thecombustion chamber. Means maybe provided for moving formof device forheating a gas supply in which the air. injector andcombustion chamberfor. the

, heating mixture are within the casing through which the main gassupply'fiows: or H '--Figure 2 is asimilar view but of .a diagrammaticcharacter of a modified form'of burner length of nine inches.

' from a diameter of inch to 1 inchesover a.

The end of the Venturi part remote from the throat is externallythreaded and is connected with a combustion chamber 2'! by a connectingpieceZB and a flame 'trapmay be located within the connecting piecebetweenithe throat and the part.20. The combustion chamber is attachedto a s'pidermember 29 which locates the combustion chamber cen- -trallywithin the cylindrical casing but leave it free to move axially; Locatedopposite to the combustion chamber is an igniting device designatedgenerally by the reference-3i which is mbunted within a housing 3|.

vice'comprises an velectric heating element 32 which is located in aslot 38 in a sleeve33and is nconnectedatz one end to the sleeve whichsleeve I extends through said housing. The other end of theelement isconnected to a steel rod 34 which is The igniting descrew-threaded atits extremities. The steel is carried-at;its extremities by.fiangedinsulating whichthe injector is disposed outside said-casin iz IFigure 3 shows-a modified form of constructionishown in Figure 2, inwhich the injector projects into a, combustion chamber located withinthe casing; e

. Figure 4 is yet a further modification inwhich bothsthe injectornozzle and the combustion chamber are arranged within the casing; and

F ig'urefi shows an arrangement in which the ports or passages throughwhich the gas is withdrawnfrom the casing, are located within thecasing. .1 Any of these devices may be fitted with. a .flame trap'of;the type referred to. r Referring now ,to the construction shown inFigure .1'; the gasheating device comprises a cylindrical' casing 10-having a laterally-extending gas inlet passage Hand a gas outlet passagel2 disposed nearthe 'opposite ends of the .casing.

respectively, to" which flanges are secured coverplates xl5 and H5. -Thecover-plate -l5 near'the gas inlet passage 1 I .is bored and threaded toreceive a pipe I! for the supply of compressed. air. The end of thecompressed air pipe is provided with'aninjector nozzle. l8 whichprojectsjinto one end of a Venturi passage. The Venturi passage is amade in. twomain parts l9 and 20 which: are se cured together by athreaded spigot joint- The The ends of the casing are flanged at [3 and14 injector nozzle l 8'.projects into the open end of that part IQ oftheVenturi passage which has the greater divergence. A suitable divergenceis provided by a passage whose diameter increases from Ag'inchto 2%inches over a length.of;2

inches. Secured in the open end by set screws 22 is aspider member 2|.The centre partofthe spider is internally screw-threaded to'receivethethreaded "end of the compressed airpipe I! to, t which itis' securelylocked. The pipe'may be roe.

tated'by an-adjusting handle 23whereby, the distance' between theopenend of the. venturi.(|9)- andthe "back plate (I5) can be adjusted; the

required adjustment may be maintained by: the

lock-nut 26, which bear against the cover-plate.

l5. The part 20 of the Venturi which isformed divergeszasit extends awayfrom the throat bushes 36 which are held incover-plates '35se-3 cured tothe ends of the sleeve- 33. The steel rod ,is prevented fromendwisemovement by nuts 31 which. bear against the-flanges oftheinsulating,

bushes. Terminal nuts3.9- are 'provided'on'the steel rod forestablishing an electrical connection with the electric element;Similarly, nuts 40 areprovided for connecting the steel rod to a sourceof electric supply. The steel rod is encircled within thesleeve 33.by aglass tube4l or by a tube of some other suitable insulating material.

The housing -3| is provided with a gland .42. for holding-the outerend-of the sleeve in position,

9 while the inner end is passed througha clear- Lance hole in thecock.43 whichis used to shutoff the gas when the igniting deviceis-withdrawn; In order that the electrical element may 'becorrectlylocated opposite the combustion chamber. the sleeve 33 is provided witha locating collar 44 t which. may be slid along it and securedin thedesired position -byda, grub-screw 45, the sleeve is then slid into thehousing until the .locating col-- lar abuts against the gland 42. v s IThe operation of the device is as follows; .j.

Assuming a fiow of gas is taking place through the. cylindrical casingaround the outside of the Venturi tube from the inlet-pipe H tothe-outlet pipeftZ, andthatthe gap betweenthe part of theventuri l 9 andthe back plate I5. is closed; the burner maybe lighted'by switching onthe electric supply to the heating element 32after which the compressedair supplied through the pipe ll is slowly. turned on. As soon astheflame appears (as seen'throu'gh the sight glass 56 and cock 5'!) theigniting deviceis withdrawn and the cook 43 closed. The burner is thenrotated by means of thefhandle 23 so as to separate the venturi' l9 sfrom the back plate I'5"until therequired volume'of gas is being drawnintothe burner. "This causes the flame 'to retrea t into thecombustionchamber 21 where it burns .in'a stable manner without formation of sootIf the mixture of gas and air which is being supplied to the combustionchamber still contains anexcess of air some secondary combustion willcontinue to take place atthe mouth "of theburner but as a rule this alsodoes'not form any soot. i

"Referring now to the construction shownin Fi e 2, the injector nozzlel8 of the compressed air pipe "is located outside the-cylindrical casingl0, within an inlet chamber; "I'hexinlet chamber communicates through a:mixing pas with'the aforesaid throat 24 has a passage which.

sage 48 with: a combustion cl'iamber 1.49 located within the casing-10.;The mixing passage-is;

formed in two parts having flanges 50 and which are secured on eitherside ofv the coverplate 15, which cover-plate is provided with anorifice 52 which forms a part of the mixing passage. The mixing passagediverges on either side of said orifice and may be separated from'thecombustion chamber by any suitable type of flame I chamber 49 and meansare provided for removing the igniting wire out of the stream of hotgas, by rotating the plug on which it is carried. With this arrangementalso the flame is mostly confined to the combustion chamber from whichthe hot products of combustion flow into the main gas stream and heatit.

In the arrangement shown in Figure 3, the mixing passage 48 is providedwith a nozzle 55 which extends into the combustion chamber 49.

In the construction shown in Figure 4, the end of the combustion chamber49 within the casing is formed with an inlet chamber 41 anda Venturipassage 55 into which the nozzle l8 of the compressed-air pipe I!projects. s

In the construction shown in Figure 5, the Venpendently connecting theexterior'end with the gas conduit, a second conduit arranged whollyoutside the gas conduit, and having an end directed into saidexteriorend of. the first said conduit and of smaller bore so as to forman injector whereby compressed air maybe injected into the first conduitto producethe injector ac= tion, and igniting means mounted adjacent tothe first said end of the first said conduit within the gas conduit. 1 t

4. An apparatus for heating an inflammable gas stream comprising agasconduit, a second conduit, provided with a throat having a divergentbore on each side thereof arranged with at least one open end within thegas conduit, said turi passage and inlet chamber are dispensed with andinjector nozzle 18 projects, directly into the combustion chamber. Thecombustion chamber is provided with a number of inlet holes 48 near thatend thereof which is attached to the cover-plate l5. The injector nozzleis arranged near the inlet holes 48 through which the gas in the casingI0 is drawn into the combustion chamber.

We claim:

1. An apparatus for heating an inflammable gas stream comprising a gasconduit,a second conduit, which second conduit is arranged with at leastone open end within the. gas conduit, said end having igniting meansadjacent thereto the other end having an opening in communication withsaid gas conduit to conduct gas from the gas conduit to the secondconduit, a third conduit having at least a part thereof outside said gasconduit and having an open end directed into said other end of thesecond conduit so as to form i an injector and of smaller bore than thatend whereby compressed air may be injected into the second conduit toproduce the injector action.

2. An apparatus for heating an inflammable gas stream within a gasconduit, comprising an open-ended first conduitdisposed wholly withinthe gas conduit, a second conduit arranged partly in and partly out ofthe gas conduit, the inner end of said second conduit being directedinto an open end of the first conduit so as to form an injector, andhaving a bore of smaller'size than that of the end into which it isdirected whereby compressed air may be injected into the first conduitto produce the injector action, and igniting means mounted adjacent tothe other end of the first said conduit.

3. An apparatus for heating an inflammable gas stream within a gasconduit, comprising a first conduit having an open end thereof arrangedend having ignition means adjacent thereto, the other end having-anopening in communication with the gas conduit to conduct gas from saidgas conduit to the second conduit on that side of the throat remote fromsaid open end, a third conduit having at least a part thereof outsidesaid gas conduit and having an openend directed into said throat anditself having a smaller bore so as to form an injector wherebycompressed air may be injected into the second conduit to produce theinjector action.

5. An apparatus for heating an inflammable gas streamwithin a gasconduit, comprising a first conduit disposed wholly within the gasconduit and having one end open and the other closed by a wall of thegas conduit, a throat adjacent to the closed end providing aspace nearthe closed end, means for connecting said space with the gas conduit, asecond conduit arranged to extend through the wall of the gas conduitinto said space, and having a bore smaller than said throat into whichit is directed soas to form an injector, and igniting means adjacenttothefirst said end of the first conduit.

6. An apparatus for heating an inflammable gas stream'within a gasconduit, comprising a first conduit disposed wholly within the gasconduit, one end of which first conduit is open and the other is closedby a wall of the gas conduit,

. the openings in the walls thereof, the bore of which second conduit issmaller than that of the first conduit so as to form aninjector, andigniting means mounted adjacent to the first said end of said conduit.

7. An apparatus for heating an inflammable gas stream comprising a gasconduit, a second conduit arranged with the gas conduit so that at leastone open end'thereof is within thegas conduit, said end having ignitionmeans adjacent thereto, the other end having an opening in communicationwith said gas conduit to conduct gas from the gas conduit to the secondconduit, means for controlling the rate of flow of the conducted gas,

a third conduit extending into said other end of the second conduit, thebore of which third conduit is smaller than that of the first conduit soas to form an injector whereby compressed air. may beinjected into thesecond conduit to produce an injector action.

LEONARD SILVER. MICHAEL MACCORMAC.

withinthe gas conduit and the other end being closed and outside theconduit, means for inde-

